CN107681681A - A kind of system-level control method of the MTDC transmission system based on VSC - Google Patents
A kind of system-level control method of the MTDC transmission system based on VSC Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
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- H02J3/36—Arrangements for transfer of electric power between AC networks via a high-tension DC link
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for AC mains or AC distribution networks
- H02J3/36—Arrangements for transfer of electric power between AC networks via a high-tension DC link
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
本发明公开了一种基于VSC的多端直流系统的系统级控制方法，包括以下步骤：获取多端直流系统中换流站的参考电压Uref及参考功率Pref，再根据多端直流系统中换流站的参考电压Uref及参考功率Pref计算多端直流系统中换流站的直流功率Pd，然后根据多端直流系统中换流站的直流功率Pd控制多端直流系统的系统级，完成基于VSC的多端直流系统的系统级控制，其中，多端直流系统中换流站的直流功率Pd为：Pd＝K(Ud‑Uref)3+Pref，其中，K为多端直流系统中换流站的控制系数，Ud为多端直流系统中换流站的直流电压，该方法能够在换流站功率变化量较大时维持系统电压稳定，避免系统直流电压越限。
The invention discloses a system-level control method of a VSC-based multi-terminal direct current system, comprising the following steps: obtaining the reference voltage U ref and the reference power Pref of a converter station in the multi-terminal direct current system, and then according to the The reference voltage U ref and reference power P ref calculate the DC power P d of the converter station in the multi-terminal DC system, and then control the system level of the multi-terminal DC system according to the DC power P d of the converter station in the multi-terminal DC system, and complete the VSC-based System-level control of the multi-terminal DC system, where the DC power P d of the converter station in the multi-terminal DC system is: P d =K(U d ‑U ref ) 3 +P ref , where K is the converter station in the multi-terminal DC system The control coefficient of the station, U d is the DC voltage of the converter station in the multi-terminal DC system. This method can maintain the stability of the system voltage when the power variation of the converter station is large, and avoid the DC voltage of the system from exceeding the limit.
Description
技术领域technical field
本发明属于电力系统控制领域，涉及一种基于VSC的多端直流系统的系统级控制方法。The invention belongs to the field of power system control, and relates to a system-level control method of a VSC-based multi-terminal direct current system.
背景技术Background technique
社会经济的发展对输电系统提出了新的要求，现有的交流输电技术在大容量输电、系统稳定等方面存在着劣势。另一方面，伴随着新能源的大规模开发，具有高不确定性的电源接入电网，对电网的调度、控制均提出了挑战。因此在传统的交流输电与直流输电技术之外，需要新的输电技术。The development of social economy puts forward new requirements for the power transmission system, and the existing AC power transmission technology has disadvantages in terms of large-capacity power transmission and system stability. On the other hand, with the large-scale development of new energy sources, the power supply with high uncertainty is connected to the power grid, which poses challenges to the dispatching and control of the power grid. Therefore, in addition to the traditional AC and DC transmission technologies, new power transmission technologies are needed.
经过多年的发展，柔性直流输电在交流电网异步互联、风电场并网、海上平台供电、城市负荷中心供电等领域已经得到了广泛的应用。柔性直流输电技术在继承了基于电流源换流器的传统直流输电技术相对于交流输电的优势之外，还有着1)控制灵活；2)没有换相失败问题；3)谐波含量小；4)网络拓扑结构更为灵活等优势。柔性直流输电技术更容易构成多端。After years of development, flexible DC transmission has been widely used in the fields of asynchronous interconnection of AC power grids, wind farm grid connection, offshore platform power supply, and urban load center power supply. In addition to inheriting the advantages of the traditional DC transmission technology based on current source converters over AC transmission, the flexible DC transmission technology also has 1) flexible control; 2) no commutation failure problem; 3) small harmonic content; 4 ) network topology is more flexible and other advantages. Flexible DC transmission technology is easier to form multiple terminals.
多端柔性直流系统(VSC-MTDC)涉及多个换流站，其控制、运行等方面的问题与两端的直流输电系统相比更加复杂，不同换流站与其对应的交流系统之间存在功率交换，换流站之间的电气量之间存在着电气耦合，由此带来的换流站之间的配合问题亟待解决。尽管VSC-MTDC存在成本高、换流站损耗大的缺点，但随着科技的进步将会有所改善。The multi-terminal flexible DC system (VSC-MTDC) involves multiple converter stations, and its control and operation issues are more complicated than those of the DC transmission system at both ends. There is power exchange between different converter stations and their corresponding AC systems. There is an electrical coupling between the electrical quantities between the converter stations, and the resulting coordination problem between the converter stations needs to be solved urgently. Although VSC-MTDC has the disadvantages of high cost and large converter station loss, it will be improved with the advancement of technology.
现有的多端柔性直流输电系统级控制方法主要有三种：主从控制、电压裕度控制以及下垂控制。There are three main control methods in the existing multi-terminal flexible DC transmission system level: master-slave control, voltage margin control and droop control.
1)主从控制：主从控制的核心在于在多端系统中，通过设置一个定电圧的主换流站来控制整个系统的电压，其余各站作为从站，定功率。在主换流站发生故障或因故退出运行时，将主换流站切换到从换流站，代替原来的主换流站进行直流电压控制。1) Master-slave control: The core of master-slave control is that in a multi-terminal system, a main converter station with constant voltage is set to control the voltage of the entire system, and the other stations act as slave stations with constant power. When the main converter station fails or is out of operation for some reason, the main converter station is switched to the secondary converter station to replace the original main converter station for DC voltage control.
2)电压裕度控制：电压裕度控制与主从控制相比，多设置一个备用的定电压主控站，主控站仍然设置为定电压控制，备用站的定电压指令值与主控站定电压指令值有一定的裕度。在主控站因为故障退出运行时，备用站能够自动切换为主控站。2) Voltage margin control: Compared with the master-slave control, the voltage margin control needs to set a spare constant voltage master control station, the master control station is still set to constant voltage control, and the constant voltage command value of the spare station is the same as that of the master control station. There is a certain margin for the constant voltage command value. When the main control station exits due to failure, the backup station can automatically switch to the main control station.
3)电压下垂控制：电压下垂控制策略借鉴了交流系统的频率下垂控制，随着换流站直流功率的增加，换流站直流电压随之下降。在系统中可以将多个换流站设置为电压下垂控制，共同调节系统电压。当有一站因故障切除时，下垂控制策略能够使得换流站自动将系统的直流电压与功率调整到平衡状态，这一过程不需要换流站之间的通信，可靠性较高。同时，由于给出的电压-功率曲线是连续的，相对于主从控制与电压裕度控制的阶梯变化，系统受到的冲击更小。3) Voltage droop control: The voltage droop control strategy is based on the frequency droop control of the AC system. As the DC power of the converter station increases, the DC voltage of the converter station decreases accordingly. In the system, multiple converter stations can be set to voltage droop control to jointly adjust the system voltage. When a station is disconnected due to a fault, the droop control strategy can enable the converter station to automatically adjust the DC voltage and power of the system to a balanced state. This process does not require communication between the converter stations and has high reliability. At the same time, because the given voltage-power curve is continuous, compared with the step change of master-slave control and voltage margin control, the impact on the system is smaller.
对于应用电压下垂控制的换流站，其功率变化量与电压变化量成比例。当换流站功率变化量较大时，换流站电压的线性变化也会很大，进而导致系统电压大幅变化，并可能引起电压越限。为缓解这一问题，需要将下垂控制曲线的斜率设置得较小。而这又会使得功率变化小时换流站调节能力的减弱。当功率变化量较小，处于换流站控制策略的调节范围之内不至于引起换流站的电压或功率越限时，电压下垂控制能够自动根据系统功率的变化进行电压的调节达到平衡并维持系统电压稳定，这一点相对于裕度控制与主从控制有着优势。For a converter station using voltage droop control, the power variation is proportional to the voltage variation. When the power variation of the converter station is large, the linear change of the voltage of the converter station will also be large, which will lead to a large change in the system voltage and may cause the voltage to exceed the limit. To alleviate this problem, the slope of the droop control curve needs to be set smaller. And this will weaken the adjustment ability of the converter station when the power changes small. When the power variation is small and within the adjustment range of the control strategy of the converter station so as not to cause the voltage or power of the converter station to exceed the limit, the voltage droop control can automatically adjust the voltage according to the change of the system power to achieve balance and maintain the system The voltage is stable, which has advantages over margin control and master-slave control.
发明内容Contents of the invention
本发明的目的在于克服上述现有技术的缺点，提供了一种基于VSC的多端直流系统的系统级控制方法，该方法能够在换流站功率变化量较大时维持系统电压稳定，避免系统直流电压越限。The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art, and provide a system-level control method for a multi-terminal DC system based on VSC. The voltage exceeds the limit.
为达到上述目的，本发明所述的基于VSC的多端直流系统的系统级控制方法包括以下步骤：In order to achieve the above object, the system-level control method of the VSC-based multi-terminal DC system according to the present invention includes the following steps:
根据给定的系统运行方式以及换流站容量获取多端直流系统中换流站的参考电压Uref及参考功率Pref，计算多端直流系统中换流站的系数K，得换流站直流电压Ud与直流功率Pd的函数关系，完成基于VSC的多端直流系统的系统级控制，其中，多端直流系统中换流站的直流功率Pd为：Obtain the reference voltage U ref and reference power P ref of the converter station in the multi-terminal DC system according to the given system operation mode and the capacity of the converter station, calculate the coefficient K of the converter station in the multi-terminal DC system, and obtain the DC voltage U of the converter station The functional relationship between d and DC power P d completes the system-level control of the VSC-based multi-terminal DC system, where the DC power P d of the converter station in the multi-terminal DC system is:
Pd＝K(Ud-Uref)3+Pref。P d =K(U d −U ref ) 3 +P ref .
根据多端直流系统中换流站的参考电压Uref和参考功率Pref以及系统运行的电压约束和功率约束计算多端直流系统中换流站的系数K。The coefficient K of the converter station in the multi-terminal DC system is calculated according to the reference voltage U ref and the reference power Pref of the converter station in the multi-terminal DC system, as well as the voltage constraint and power constraint of the system operation.
本发明具有以下有益效果：The present invention has the following beneficial effects:
本发明所述的基于VSC的多端直流系统的系统级控制方法在具体操作时，通过多端直流系统中换流站的控制系数K使得正常运行状态下直流电压与直流功率按照输电系统的运行要求与换流站的额定功率来确定。同时由于直流电压的变化为非线性的，当直流功率与参考点的偏移量较大时，电压也不会有较大的变化，从而达到在换流站功率变化量较大时维持系统电压稳定的目的，避免系统直流电压越限的问题。In the specific operation of the system-level control method of the VSC-based multi-terminal DC system described in the present invention, the control coefficient K of the converter station in the multi-terminal DC system is used to make the DC voltage and DC power in the normal operating state comply with the operating requirements of the transmission system and The rated power of the converter station is determined. At the same time, since the change of DC voltage is nonlinear, when the offset between the DC power and the reference point is large, the voltage will not change greatly, so as to maintain the system voltage when the power change of the converter station is large The purpose of stability is to avoid the problem that the DC voltage of the system exceeds the limit.
附图说明Description of drawings
图1为本发明的控制策略方程图；Fig. 1 is the control strategy equation figure of the present invention;
图2为本发明中实施例一的网络拓扑图；Fig. 2 is the network topological diagram of embodiment one among the present invention;
图3为下垂控制下换流站2及换流站3的功率曲线图；Fig. 3 is a power curve diagram of converter station 2 and converter station 3 under droop control;
图4为下垂控制下换流站1及换流站4的功率曲线图；Fig. 4 is a power curve diagram of converter station 1 and converter station 4 under droop control;
图5为下垂控制下各换流站的电压曲线图；Fig. 5 is a voltage curve diagram of each converter station under droop control;
图6为改进控制策略下换流站2及换流站3的功率曲线图；Fig. 6 is a power curve diagram of converter station 2 and converter station 3 under the improved control strategy;
图7为改进控制策略下换流站1及换流站4的功率曲线图；Fig. 7 is a power curve diagram of converter station 1 and converter station 4 under the improved control strategy;
图8为改进控制策略下各换流站的电压曲线图。Fig. 8 is the voltage curve of each converter station under the improved control strategy.
具体实施方式detailed description
下面结合附图对本发明做进一步详细描述：The present invention is described in further detail below in conjunction with accompanying drawing:
参考图1，本发明所述的基于VSC的多端直流系统的系统级控制方法包括以下步骤：Referring to FIG. 1, the system-level control method of the VSC-based multi-terminal DC system according to the present invention includes the following steps:
根据给定的系统运行方式以及换流站容量获取多端直流系统中换流站的参考电压Uref及参考功率Pref，计算多端直流系统中换流站的系数K，得换流站直流电压Ud与直流功率Pd的函数关系，完成基于VSC的多端直流系统的系统级控制，其中，多端直流系统中换流站的直流功率Pd为：Obtain the reference voltage U ref and reference power P ref of the converter station in the multi-terminal DC system according to the given system operation mode and the capacity of the converter station, calculate the coefficient K of the converter station in the multi-terminal DC system, and obtain the DC voltage U of the converter station The functional relationship between d and DC power P d completes the system-level control of the VSC-based multi-terminal DC system, where the DC power P d of the converter station in the multi-terminal DC system is:
Pd＝K(Ud-Uref)3+Pref。P d =K(U d −U ref ) 3 +P ref .
其中，根据多端直流系统中换流站的参考电压Uref和参考功率Pref以及系统运行的电压约束和功率约束计算多端直流系统中换流站的系数K。Among them, the coefficient K of the converter station in the multi-terminal direct current system is calculated according to the reference voltage U ref and the reference power Pref of the converter station in the multi-terminal direct current system and the voltage constraints and power constraints of the system operation.
实施例一Embodiment one
图2为四段系统的拓扑，系统参数如表1、表2及表3所示：Figure 2 is the topology of the four-segment system, and the system parameters are shown in Table 1, Table 2 and Table 3:
表1Table 1
表2Table 2
表3table 3
结果证明，本发明具有稳定电压的能力。The result proves that the present invention has the ability to stabilize voltage.
在pscad中进行的暂态仿真结果也说明了改控制策略对于稳定电压、功率的作用。The transient simulation results carried out in pscad also illustrate the effect of the modified control strategy on stabilizing voltage and power.
最后应当说明的是，以上实施例仅用以说明本发明的技术方案，本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的范围内，根据本发明的技术方案及其发明构思加以等同替换或改变，都属于本发明的保护范围。Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent replacement or change of the technical solution and its inventive concept all belong to the protection scope of the present invention.
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